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Free keywords:
Transient Electromagnetic; Induced Polarization; Inversion
Abstract:
Transient electromagnetic (TEM) data can be significantly distorted by induced polarization
(IP) effect, leading to a sign reversal feature and, if overlooked, false geological interpretation.
The aim of this paper is to incorporate IP effects in the forward modelling and recover the
distorted TEM data using an efficient inversion algorithm. To achieve this aim, we developed a
1D forward solver to incorporate the IP effects using various IP parameterizations including
Cole-Cole, maximum phase angle (MPA), maximum imaginary conductivity (MIC) (Fiandaca
et al., 2018) and the Jeffrey transform of Cole-Cole parameters (Ghorbani et al., 2007). For 1D
inversion of distorted TEM data we used Levenberg-Marquardt and very fast simulated
annealing algorithms. The result of 1D forward calculation and inversion of synthetic IPdistorted
TEM data revealed that, for incorporation the IP effects into the TEM data, the Cole-
Cole parametrization is more robust and reliable than MPA, MIC, and Jeffrey transform.
Moreover, the result of inversion using Levenberg-Marquardt algorithm is strongly depends on
the starting model. We successfully implemented these algorithms for 1D inversion of
synthetic IP-affected TEM data (Fig. 1 ). For synthetic data generation, a 3-layered half space
model with the thickness of the first and second layers of 5 m was considered. The resistivities
of the layers from top to bottom are 10, 5 and 300 Ωm, respectively. To include the IP effect,
second layer considered to be chargeable with Cole-Cole parameters of m = 0.5, τ = 0.01 s and
c = 0.5. TEM central-loop configuration with a loop size of 50*50 m2 and step-off current of 1
A with a zero ramp time was used for data simulation. We evaluated the performance of our
algorithm using field data, successfully.
